The present invention relates to a humidifier.
The invention has been developed primarily for use with a breathable gas supply apparatus in Continuous Positive Airway Pressure (CPAP) treatment of, for example, Obstructive Sleep Apnea (OSA) and other ventilatory assistance treatments such as Non Invasive Positive Pressure Ventilation (NIPPV) and will be described hereinafter with reference to these applications. However, it will be appreciated that the invention is not limited to these particular fields of use and also finds application in, for example, assisted respiration, mechanical ventilation and the like.
CPAP treatment is a common ameliorative treatment for breathing disorders including OSA. CPAP treatment, as described in U.S. Pat. No. 4,944,310, provides pressurised air or other breathable gas to the entrance of a patient""s airways at a pressure elevated above atmospheric pressure, typically in the range 4-20 cm H2O.
It is also known for the level of treatment pressure to vary during a period of treatment in accordance with patient need, that form of CPAP being known as automatically adjusting nasal CPAP treatment, as described in U.S. Pat. No. 5,245,995.
NIPPV is another form of treatment for breathing disorders which can involve a relatively higher pressure of gas being provided in the patient mask during the inspiratory phase of respiration and a relatively lower pressure or atmospheric pressure being provided in the patient mask during the expiratory phase of respiration.
In other NIPPV modes the pressure can be made to vary in a complex manner throughout the respiratory cycle. For example, the pressure at the mask during inspiration or expiration can be varied through the period of treatment, as disclosed in the applicant""s international PCT patent application No. PCT/AU97/00631.
Typically, the ventilatory assistance for CPAP or NIPPV treatment is delivered to the patient by way of a nasal mask. Alternatively, a mouth mask or full face mask or nasal prongs can be used. In this specification any reference to a mask is to be understood as incorporating a reference to a nasal mask, mouth mask, full face mask or nasal prongs.
In this specification any reference to CPAP treatment is to be understood as embracing all of the above described forms of ventilatory treatment or assistance.
Breathable gas supply apparatus broadly comprise a flow generator constituted by a continuous source of air or other breathable gas generally in the form of a blower or driven by an electric motor. The electric motor driving the blower is typically controlled by a servo-controller under the control of a micro controller unit. A hospital piped supply can also be used. The gas supply is connected to a conduit or tube, which in turn is connected to a patient mask which incorporates, or has in close proximity, an exhaust to atmosphere for venting exhaled gases.
In order to prevent drying of the patient""s airways during use of a breathable gas supply apparatus it is known to pass the gas through a humidifier before supplying the gas to the patient. Humidification is achieved by passing the air over a water surface within a humidifier so that the gas absorbs moisture from the water before being delivered to the patient. The two main types of humidifier are passive, where the water is not heated, and active, where the water is heated.
A known passive humidifier is the applicant""s Passover (Trade Mark) humidifier. Other passive humidifiers are disclosed in U.S. Pat. Nos. 5,231,979, 5,537,997 and 5,598,837.
A known active humidifier is the applicant""s HumidAire (Trade Mark) which heats the water in the humidifier via a thermostatically controlled electric heating element. The temperature of the water is set manually by the patient. The HumidAire humidifier also has a built in safety feature to prevent the heater element reaching excessive temperatures under fault conditions.
European patent application No. EP 0845277 discloses an active humidifier that includes a thermostatically controlled electric heating plate. Active humidifiers are also disclosed in U.S. Pat. Nos. 4,621,632 and 4,203,027.
A disadvantage of known active humidifiers is the expense of the heating elements and associated thermostatic temperature control equipment.
A disadvantage of known passive humidifiers is an inability to easily vary the amount of humidification of the gas.
It is an object of the present invention to substantially overcome or at least ameliorate one or more of the above disadvantages.
Accordingly, in a first aspect, the present invention provides a humidifier for use with a breathable gas supply apparatus, said humidifier comprising:
a hollow body adapted for partial filling with water up to a predetermined maximum water level;
a gas inlet to the body above the maximum water level;
a gas outlet from the body above the maximum water level; and
a constant temperature heating element for heating the water.
In one embodiment, the heating element is disposed within the body.
In another embodiment, the heating element is disposed external the body.
In a second aspect, the present invention provides a humidifier for use with a breathable gas supply apparatus, said humidifier comprising:
a hollow body adapted for partial filling with water to a predetermined maximum water level;
a gas inlet to the body above the maximum water level;
a gas outlet from the body above the maximum water level;
means to heat the water, in the body; and
an adjustable flow divider adapted to divide the interior of the body above the maximum water level into a relatively dry gas region and a relatively wet gas region, wherein the position of the divider is variable so as to vary the relative proportion of the gas flowing from the inlet to the outlet that passes through the relatively dry and relatively wet gas regions to thereby vary the amount of humidification thereof.
Preferably, the position of the divider is variable between a first position in which all of the gas is diverted to the relatively wet gas region for maximum humidification, and a second position in which all of the gas is diverted to the relatively dry gas region for minimum humidification.
The heating means is preferably a constant temperature heating element, such as a self regulating wire.
The humidifier desirably also includes a storage reservoir adapted to replenish the water in the body.
The divider preferably also includes baffle plates. The position of the baffle plates can be fixed or adjustable.
In one embodiment, the divider is a generally planar plate of substantially complimentary cross section to the interior of the body above the maximum water level. The plate preferably includes a threaded hole adapted to engage a threaded rod, wherein rotation of the rod causes the plate to move between the first and second positions. The exterior of the plate preferably forms a substantially fluid-tight seal with the interior of the body.
In another embodiment, the divider includes a first end remote the gas inlet and the gas outlet and a second end adjacent the gas inlet and the gas outlet, wherein the divider is adapted to rotate about or near the first end to cause the second end to move between the first and second positions.
In a further embodiment, the divider includes a first and second end adjacent the gas inlet and the gas outlet, wherein the divider is adapted to rotate about or near its centre to cause the first and second ends to move between the first and second positions.
In a third aspect, the present invention provides a humidifier for use with a breathable gas supply apparatus, said humidifier comprising:
a hollow body adapted for partial filling with water to a predetermined maximum water level;
a gas inlet to the body above the maximum water level;
a gas outlet from the body above the maximum water level;
a constant temperature heating element for heating the water; and
an adjustable flow divider adapted to divide the interior of the body above the maximum water level into a relatively dry gas region and a relatively wet gas region, wherein the position of the divider is variable so as to vary the relative proportion of the gas flowing from the inlet to the outlet that passes through the relatively dry and relatively wet gas regions to thereby vary the amount of humidification thereof.